A study of cancer risk in approximately 146,000 x-ray technologists who were certified by the American Registry of Radiologic Technologists between 1926-80 is ongoing. Exposures have occurred over many years, with cumulative doses for most technologists estimated to be in the range of 5-20 cGy. Overall, cancer mortality was 21% lower than expected. Neither lung cancer nor leukemia mortality were associated with number of years worked in the medical radiation field or with specific work practices. For breast cancer, there was a slight tendency of increasing risk as number of years worked increased, but this was not significant. A recently completed mortality analysis among Catholic nun technologists revealed an increased risk of breast cancer among those certified before 1940, although risk did not increase with duration of certification. Blood samples were taken from 90 technologists with documented high or low radiation film badge doses and fluorescent in situ hybridization (FISH) was used to identify stable chromosome aberrations. Age was the strongest predictor of aberration frequency. After adjusting for age, a positive (non-significant) association was found with number of years worked before 1955. Considerable overlap was observed in the aberration frequencies for high- and low-exposed individuals. To develop estimates of occupational radiation exposure for individual cohort members, collaboration with medical physicists and industrial hygienists from the National Institute for Occupational Safety and Health has recently been formalized. Additionally, an initiative was undertaken to add a renewable material source for DNA and RNA for future genetic studies. Initial efforts are focusing on women with breast plus other (multiple) primary cancers and men with testicular cancer, early-onset (<55) prostate cancer, and prostate plus other primary cancers, but will likely expand to other cancer sites. This effort will include testing for genes that may be involved in DNA repair or repair of radiation damage, such as ATM and RAD51. A cohort of 20,000 nuclear workers chronically exposed to large doses of external radiation and/or plutonium at the Mayak nuclear weapons plant in the South Ural region in Russia is being studied to evaluate cancer mortality. A paper evaluating the risk of bone cancer in this cohort is near completion, and analyses of the risk of liver cancer are underway. Analyses evaluating the effects of exposure to external radiation and plutonium on the risks of several other types of cancer are planned. In addition, data on auxiliary plant workers as potential controls are being developed. Several studies of Chornobyl clean-up workers are currently underway. Cancer incidence is being evaluated in three cohorts, comprising 17,500 clean-up workers, from Estonia, Latvia, and Lithuania who were sent to Chornobyl (Ukraine) following the reactor accident in 1986. Cohort members are interviewed to elicit other risk factor information. In addition, with support from DOE, NRC, and the French Institut de Protection et Surete Nucleaire (IPSN), NCI is in the final phase of a pilot study of leukemia and other hematologic disease among the Chornobyl clean-up workers in Ukraine. - Human Subjects & Human Subjects: Interview, Questionaires, or Surveys Only & Human Tissues, Fluids, Cells, etc.